Structure of the condenser-type microphone
Microphone can basically divided into three types, electrodynamic-type, condenser-type, and piezoelectric-type according to its conversion methods. The electrodynamic-type has well-established demand in the music world, and the piezoelectric-type is mainly used for a microphone of a low frequency sound level meter. Condenser-type is popularly used as measurement microphone. It features not only to be downsized with ease, but also to have flat frequency responses over a wide range of frequency, and provides markedly high stability. Condenser-type microphone is available in two types, bias-type and back electret-type. The difference is the way to apply the DC voltage. Bias-type is required to supply DC voltage from external. Back electret-type is affixed permanently electrically polarized polymer film to the surface of backplate in place of applying voltage. Generally, bias-type is much more sensitive and stable than back electret-type.
Operating principle of the Sound Intensity Probe
Please read "Sound and sensors" in "Ono Sokki Technical Report" for more details